Since the Wnt signaling pathway has an important role in maintenance and specification of precursor cell and stem cell lineages in development and in regeneration of a number of tissues, we theorized that it could play a similar role in the inner ear. Although mammals lack the capacity to regenerate damaged cochlear cells, increasing evidence has shown that stem cells exist in the ear and are capable of differentiation into functional hair cells. We have undertaken a study of the role of ?-catenin in precursors for hair cells during development and in inner ear stem cells. In our previous work, we demonstrated that ?-catenin increased the differentiation of inner ear stem cells to hair cells by upregulation of Atoh1 expression mediated by direct binding to the Atoh1 enhancer. These findings indicate that Atoh1 is a target gene of the Wnt signaling pathway which is mediated by ?-catenin. We hypothesize that Wnt signaling is required for inner ear progenitor cell expansion and subsequent specification, and we further hypothesize that ?-catenin is the initial cue for Atoh1 expression and hair cell formation in the auditory system. Our hypothesis will be tested in a series of studies to pursue two specific aims. In the first aim we will determine the role of Wnt/?-catenin signaling in hair cell formation during cochlear development. We will knock out ?-catenin before hair cell formation and during hair cell development along the cochlear axis. We expect that hair cell formation will be attenuated. We will further test if that ?-catenin is the initial cue for hair cell formation in the auditory system. Understanding the regulation of Atoh1 will provide insights into the development of hair cells in the embryo and may be a potential approach for hair cell regeneration and restoring hearing. In the second aim we will determine the role of Wnt/?-catenin in inner ear stem cell expansion and specification and its implication in hair cell regeneration. We will use the same ?-catenin overexpression approach in two model systems for the study of hair cell regeneration. In the first we use inner ear stem cells, which provide an in vitro system for studying the signaling that leads to hair cell formation, to evaluate the expansion and differentiation of the stem cells. The second system is an in vivo mouse model in which we will damage hair cells by exposure to sound and determine whether hair cells can be regenerated by overexpression of ?-catenin. PUBLIC HEALTH RELEVANCE: Sensory hair cells in the cochlea are responsible for sound detection but these cells can be damaged or lost by a variety of factors leading to deafness. This proposal investigates new ways to restore the hair cells by manipulation of resident inner ear stem cells, using endogenous factors for stimulation. The ultimate goal of this project is to find a noninvasive approach that could become a therapy for the treatment of sensorineural hearing loss for which there is currently no effective intervention other than hearing aids or cochlear implants.